How social is social? Saying in his slide deck that he's "sick of inviting his friends," Brad Fitzpatrick is thinking about what constitutes the "social graph." Living somewhere between existing social applications like Facebook and a fully realized semantic web, Yihong Ding, who points to a Tim Berners-Lee post on the subject, elaborates on the idea here:

The emergence of social graphs goes beyond simply cloning the
friendships we develop in the real world and placing them in a virtual
world. By contrast, the value of this emergence signals the beginning
of a great transformation of information management systems on the Web.